Not just a technical exercise but a genuine work of art, this working engine by Huib Visser employs a quartz glass cylinder so you can see combustion taking place. Watch and be mesmerized. 

Working from an original design by Jan Ridders, Huib Visser of the Netherlands built this exquisite four-stroke engine in tabletop scale. The horizontal, single-cylinder powerplant, a true treat for the eyes, is elegantly constructed in beautiful materials, but the crowning touch is the cylinder, which was crafted from quartz glass and carries a graphite piston. When the engine is running—which it does quite well, by the way—you can look directly inside and see combustion taking place.

Visser has built several of these wonderful machines in both two-stroke and four-stroke configurations, employing spark plugs and electronic ignition systems of his own design and running them on Coleman camping fuel (petroleum naptha, around 50 octane). This one, a four-stroke, uses a toothed belt running at 2:1 to drive a rotary intake/exhaust valve mechanism. Prepare to be mesmerized.